The Wolf administration said Tuesday that Pennsylvania's prison population decreased by 842 inmates last year, continuing a decline stemming from criminal justice reforms enacted in 2012, but a union leader said the numbers mask other problems.

At a news conference at the Harrisburg Community Corrections Center, Gov. Tom Wolf and Corrections Secretary John Wetzel said the reforms are reducing the number of offenders in prison and diverting parole violators to the less-expensive local centers also known as halfway houses. That saves money that can be used to educate offenders and provide treatment for drug addiction or mental health problems, they said.

Wolf, a Democrat, said it costs $41,000 a year on average to incarcerate an offender in a state prison.

"We need to make sure that we are spending these taxpayer dollars on those offenders who require that level of incarceration and not wasting money that could be used for education or job creation, which will both ultimately keep more people out of prison," he said.

The administration billed last year's decline as the biggest one-year decline in four decades, but the prison population was soaring throughout most of that period. The 2015 population, including prison inmates and offenders held in alternative settings, was 49,914 -- the smallest since 2009, the department said.

Roy Pinto, president of the Pennsylvania State Corrections Officers Association, said the numbers don't tell the whole story.

Many parole violators at local corrections centers who should have been returned to prison for infractions are instead being kept at the centers until they're released to make the program look better, Pinto said.

"They pretty much have to commit another crime or they don't come back" to prison, he said.